High-concentration mercury-containing wastes, including sludge, waste catalysts, waste fluorescent lamps, waste mercury lamps, waste amalgam and the like, which contain high concentrations of mercury, are discharged from various industrial facilities. When these mercury-containing wastes are merely classified and disposed of as toxic waste, not only can they be a major cause of soil contamination, but they can also enter groundwater via soil and threaten the aquatic ecosystem.
Since contamination of the ecosystem can lead directly to human mercury poisoning, thorough control of high-concentration mercury-containing waste is necessary. In addition, due to the Minamata International Mercury Convention (official name: Minamata Convention on Mercury), high-concentration mercury-containing waste will be controlled internationally.
In response to these international changes in the mercury control requirements, various companies and research institutes overseas have actively conducted research to develop processes and equipment for recovering mercury from high concentration mercury-containing waste and disposing of the waste as harmless waste. Also in Korea, governmental regulations on mercury-containing waste and disposal options for the waste have been actively reviewed.
Companies that manufacture systems capable of recovering mercury from mercury-containing waste include Mercury Recovery Services (MRS), Inc. (USA), Nomura Kohsan Co., Ltd. (Japan) and the like. MRS, Inc. has recovered mercury by the MR2 (Mercury Removal/Recovery) process that includes thermal desorption, gas filtering and condensation. In this regard, the process is operated at a temperature of about 700° C. to 900° C. and is performed on various wastes, including soil, catalysts, by-products from metal smelting processes, sludge from wastewater treatment, and the like.
The mercury recovery technology of Nomura Kohsan Co., Ltd. (Japan) includes a thermal treatment process employing a rotary kiln, a wet cooling process, and a mercury purification process. The thermal treatment process is operated at a temperature of about 600 to 800° C. to treat mercury-containing wastes, including waste fluorescent lamps, batteries and the like, which are discharged from various industrial facilities.
This mercury desorption process that is performed using high-temperature thermal treatment has advantages in that it is conveniently operated and can certainly lower the mercury concentration of process by-products to a value lower than the limit value. However, the mercury desorption process has disadvantages in that energy efficiency can be relatively low due to the use of relatively high temperatures and in that the durability of the apparatus is easily reduced.
In addition, in conventional technologies for recovering mercury from fluorescent lamps, waste or the like have disadvantages, a separate unit capable of additionally separating mercury generated during thermal deposition and gaseous materials other than mercury is not present. Thus, there is a disadvantage in that various gaseous impurities separated together with mercury move to a condensation state together with mercury vapor, or the impurities may also be condensed together with mercury vapor in a connection tube without moving to the condensation stage, thereby reducing recovery of mercury. In addition, there is a disadvantage in that an additional separate process needs to be performed in order to high-purity mercury.